The present invention relates generally to a compressor for use in a heating, ventilating and air conditioning system. More particularly, the present invention relates to a device and method for improving the operation of compressors used in heating, ventilating, and air conditioning systems.
In order to increase the efficiency of heating, ventilating, and air conditioning (HVAC) systems, modulating compressors have been developed. Modulating compressors allow a variation in capacity of the output of the compressor, thereby allowing HVAC systems to operate more efficiently. Some examples of modulating compressors include, but are not limited to, two-speed compressors, hot gas bypass compressors, variable speed compressors, and blocked or open suction-type compressors.
The cylinder disengagement-type compressor is known to be a particularly versatile and efficient type of modulating compressor. Reference is made to U.S. Pat. No. 6,132,177, for a more detailed understanding of cylinder-disengagement type compressors, the disclosure of which is incorporated by reference. Such a compressor operates by selectively deactivating one or more cylinders of a reciprocating compressor. In a cylinder disengagement-type compressor, a drive motor of the compressor is reversible. By reversing the motor, the capacity of one or more of the cylinders of a reciprocating compressor may be varied. This variation in capacity may be achieved by the operation of an eccentric cam on a crankpin of a compressor crankshaft. By rotating the eccentric cam in either direction relative to the crankshaft, a variation in the effective stroke length of the piston may be achieved. This variation in the stroke length yields a variation in the capacity of the affected cylinder of the compressor. As a result, the cylinder disengagement-type compressor can be extremely efficient and provide a very cost-effective way to achieve capacity modulation.
For HVAC systems requiring compressors having larger capacities such as 3-5 tons, the use of more powerful, three-phase motors for example, may be desired. Three-phase motors may often have a start-up torque having a magnitude significantly higher, often as much as three to five times higher, than the steady-state torque required to operate a compressor of a given capacity. Due to this excessive start-up torque, the angular acceleration of the crankshaft of the compressor may also be correspondingly excessive. As a result, when the three-phase motor of a cylinder disengagement-type compressor is reversed, the crankpin rotates through an arc in an unloaded condition and strikes the eccentric cam, thereby exerting a significant impact force between the crankpin and the eccentric cam. Repeated occurrences of such impact forces may reduce the reliability of the cylinder disengagement-type compressor resulting in costly maintenance and repairs. The theoretical relationship between the impact force and the crankshaft/rotor inertia in such a system is described in xe2x80x9cA Computational Model of Impact Loading in a Modulating Reciprocating Compressor,xe2x80x9d distributed in the August 2000 International Compressor Engineering Conference.
Accordingly, the present invention is directed to a device and method for reducing the impact force of a crankpin on an eccentric ring when a motor of a cylinder disengagement-type compressor is reversed. The devices and methods of the present invention reduce the impact force of the crankpin against the eccentric cam by increasing the rotational inertia of the crankshaft. Increasing the inertia of the crankshaft reduces the angular acceleration of the crankshaft, thus reducing the velocity of the crankpin as it rotates to the point of impact. Since the velocity and acceleration at the point of impact is reduced, the impact force is reduced.
At the same time, increasing the rotational inertia of the crankshaft too much can impose substantial and damaging forces on the motor mounts. The present invention preferably increases the rotational inertia of the crankshaft to a degree that increases the service life of the mechanical coupling between the crankshaft and the compressing member of the compressor, while keeping the service life of the motor mounts within an acceptable limit. Most preferably, the service life of the mechanical coupling, the motor mounts, and other service components of the compressor will all fall within an optimum service life.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly
To attain the advantages and in accordance with the purposes of the invention as embodied and broadly described herein, one aspect of the invention is directed to a variable capacity or modulating compressor for use in an HVAC system including a block defining at least one cylinder, a reversible drive shaft rotatably supported by the block, and a piston coupled to the reversible drive shaft for compressing a fluid within the cylinder. The variable capacity or modulating compressor further includes a motor added to the reversible drive shaft for rotating the reversible drive shaft, an inertia-increasing member coupled to the reversible drive shaft for reducing the acceleration of the reversible drive shaft, and a housing containing the block, the reversible drive shaft, the piston, the motor, and the inertia-increasing member, whereby the capacity of the compressor is changed upon reversal of the direction of rotation of the reversible drive shaft.
In yet another aspect, the invention provides a reciprocating drive system including a reversible drive shaft, a motor coupled to the reversible drive shaft for rotating the reversible drive shaft, and a reciprocating member coupled to the reversible drive shaft for providing a reciprocating linear displacement. The reciprocating drive system further includes a cam member coupled to the reversible drive shaft, an eccentric member coupling the cam member to the reciprocating member, and an inertia-increasing member on the drive shaft for reducing the acceleration of the reversible drive shaft, whereby the cam member and eccentric member are configured to alter the reciprocating linear displacement of the reciprocating member upon reversal of the direction of rotation of the reversible drive shaft.
In a further aspect, the invention provides a method for reducing an impact force between components in a cylinder disengagement-type compressor including a block defining at least one cylinder, a reversible drive shaft rotatably supported by the block, a piston coupled to the drive shaft for compressing a fluid within the cylinder, a motor coupled to the reversible drive shaft for rotating the reversible drive shaft, and a housing containing the block, the reversible drive shaft, the piston, and the motor, whereby the capacity of the cylinder disengagement-type compressor is changed upon reversal of the direction of rotation of the reversible drive shaft. The method includes increasing the inertia of the reversible drive shaft by including an inertia-increasing member to the reversible drive shaft, said inertia-increasing member being sized to reduce to a safe level the acceleration of the reversible drive shaft upon start-up or reversal of the direction of rotation of the reversible drive shaft.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.